The operation of industrial equipment such as assembly lines, machine tools and processing equipment is often governed by an automation controller in accordance with a stored program. In conventional automation controllers, the control program is stored in a memory and includes instructions which are read out in rapid sequence and executed to examine the condition of selected sensing devices on the controlled equipment, or to energize or de-energize selected operating devices on the controlled equipment contingent on the status of one or more of the examined sensing devices.
Large controllers typically consist of a number of modules with different functions assigned to each module. For example, one module may execute the user control program, another may interface the controller to the remote sensing and operating devices, and yet another module may control communications with a host computer via a local area network. This arrangement permits one or more human operators to monitor and control an industrial process via computer workstations.
As part of this monitoring process, it is desirable that the control program be capable of presenting the human operator with some type of representation of the parameters of the various sensing devices associated with a given industrial process. Such a representation (hereinafter, a "tag") would enable an operator to, for example, specify a set of sensing devices for which parameter measurements would be displayed by the control program. Unfortunately, display and selection of the various tags associated with a given industrial process is communicated by the fact that proprietary software is currently utilized to provide interfaces for such tags. Accordingly, an industrial control program needs to include code peculiar to each type of tag for which parameter measurements are to be displayed by the control program. In addition, mechanisms are not available for centralized monitoring of the tags representative of sensing devices monitored by more than one industrial control program.